An intensive investigation of oxygen-dependent unsaturated fatty acid biosynthesisis being undertaken using several species of bacilli and other bacteria as experimental organisms. It is hoped that this study will elucidate the following: 1. The mechanisms by which these organisms adaptively adjust the level of unsaturated fatty acids in their membrane lipids in response to changes in environmental temperature and other environmental and biochemical factors. 2. The specific roles played by unsaturated fatty acids, primarily as components of complex lipids, in the synthesis and temperature - induced modification of the bacterial cell membrane. 3. The mechanisms of hydrogen removal in desaturation and the factors which control the positional specificity of double-bond insertion and substrate specificity for the desaturation enzyme. The research will be carried out using both whole cells in conjunction with metabolic inhibitors and radioactive tracers and with cell-free preparations isolated enzymes using labeled substrates.